Twin piston pneumatic spring



April 23, 1968 R. J. HENNELLS 3,379,430

TWIN PISTON PNEUMATIC SPRING Filed Jan. 17, 1966 INVENTOR. PANSOM J. HENA/ELLS AFTOP/VH S United States Patent 3,379,430 TWIN PISTGN PNEUMATIC SPRING Ransom J. Henneils, Plymouth. Mich, assignor to W. E.

Henneiis Company, Inc, Bellevilie, Mich, a corporation of Michigan Filed Jan. 17, 1966, Ser. No. 521,194 7 Elaims. (1. 267--64) ABSTRACT OF THE DISCLOSURE A pneumatic spring for cushioning loads having a main cylinder housing and two coaxial pistons connected together by means defining a movable piston unit slideably disposed in said main cylinder housing. Wall means are located internally of said piston unit dividing it into two interdependent fluid-tight chambers. The first of said fluidtight chambers has means providing communication therefrom to the atmosphere. The second of said fluid-tight chambers has means providing communication therefrom to the main cylinder housing such that when the pressure fluid, such as air emanating from a single source is applied to both pistons simultaneously, the force applied to the piston unit is thereby doubled. Release of said mechanical load applied to the piston unit will permit said piston unit to automatically return to its original position due to the elasticity of the fluid contained therein.

This invention relates to pneumatic springs such as those used in metal forming presses and it relates particularly to a pneumatic spring having twin pistons for maximizing the force resisting strength of the spring.

The use of pneumatic springs in connection with metal forming presses has been well known for a number of years and a highly successful type thereof is illustrated by my Patent No. 3,101,194, issued Aug. 20, 1963. For larger presses, however, it has in the past been necessary to use an unreasonable number of such springs to provide the desired resistive force, or it has been necessary to utilize combined pneumatic and hydraulic springs. Both of these alternatives have been recognized by those skilled in the art as undesirable in that the use of a large number of springs increases the initial cost outlay and maintenance and operation expenses, whereas the use of combined pneumatic and hydraulic springs requires more space be tween the press platens than is needed for press purposes and hence presents much wasted space and additional and undesired costs of machining to place the combined springs into presently known presses.

It is therefore among the objects of the invention:

(1) To provide a pneumatic spring having a greater capacity for resistance to compression than presently known pneumatic springs without an excessive increase in the cost thereof and without appreciable, if any, increase in the axial length thereof.

(2) To provide a pneumatic spring as aforesaid which can be conveniently utilized in the same manner as previously known pneumatic springs.

(3) To provide a pneumatic spring as aforesaid which will not require appreciable modification in the design of presses in which they are to be used, which presses are using the presently known pneumatic springs.

(4) To provide a pneumatic spring as aforesaid whose maintenance is substantially similar to the maintenance of presently known pneumatic springs.

(5) To provide a pneumatic spring as aforesaid which will have the resistive force at least approaching that of conventional pneumatic-hydraulic springs but will be free from the danger of malfunctioning in the event of leakage of resistive fluids.

(6) To provide a pneumatic spring as aforesaid which "ice will have the resistive capacity of presently known pneumatic-hydraulic springs but does not use hydraulic fluid.

Other objects and purposes of the invention will be ap parent upon reading the following specification and examining the accompanying drawings, in which:

FIGURE 1 is a central longitudinal sectional view illustrating the invention in the unloaded position.

FIGURE 2 is a sectional view similar to FIGURE 1 illustrating the invention in the loaded position.

For convenience of description, the terms upper, lower and words of similar import will have reference to the device of the invention as appearing in FIGURES 1 and 2. The terms inwardly, outwardly and derivatives thereof will have reference to the geometric center of said device.

General description In general, the apparatus embodying the invention comprises a main cylinder housing having positioned therein two coaxial pistons connected together by rigid means defining a movable piston unit having an internal fluid chamber, wall means axially spaced from the top of said cylinder within said chamber dividing it into two interdependent fluid-tight chambers, means providing communication from one of said pair of fluid-tight chambers to the main cylinder housing such that when the pressure fluid, such as air emanating from a single source, is applied to both pistons simultaneously, the force applied to the piston unit is thereby doubled. Thus, when a mechanical load is applied to the piston unit and the source of fluid pressure is applied thereto as aforesaid, the force resisting said load is approximately double over that available from pistons presently known.

Detailed construction A pneumatic spring 10 (FIGURE 1) comprises a first reservoir 11 and a second reservoir 12 interconnected by a passageway 13. The cross section of the pneumatic spring, in this embodiment, is shown to be circular, however, it is contemplated that other cross sections are just as advantageous and, therefore, the illustrated embodiment hereinafter described is not intended to be limiting.

More particularly, the first reservoir 11 (FIGURE 1) is formed by a primary housing 16 which in this embodiment is of two diameters and has a cylindrical side wall 17, a top wall 18 and an open end 19. An opening 21 in the side wall 17 is axially spaced from the top wall 18 a distance which will later become apparent and permits communication from the annular clearance 34 to the atmosphere. A bushing or guide member 22 is rigidly fixed to the side wall 17 and positioned adjacent the open end 19. An O-ring 31 forms a seal between the bushing 22 and the cylindrical shell 29.

The cup-shaped housing 16 is equipped with a check valve assembly 14, which may be similar to that disclosed in my Patent No. 3,101,194, issued Aug. 20, 1963, for permitting air to enter into the interior of the first reservoir 11, but will not permit air to exit therefrom into the supply line, thereby preventing surges of air back into the supply line 15.

A coaxial hollow post member 23 is rigidly fixed to the top wall 18 and extends downwardly a distance substantially equal to the length of the cylindrical side wall 17. A flange extension 26 is rigidly secured to the hollow post member 23 at its lowermost end and extends radially outwardly to a diameter which will later become apparent.

The piston unit 38 comprises a pair of pistons 27 and 28 rigidly held together in an axially spaced relationship by a cylindrical shell 29. Piston 27 is fastened to the inner surface of the cylindrical shell 29 by a pair of annular keys or snap rings 30. A coaxial opening in the piston 27 is designed for a slideable fit over the hollow post mem- 3 her 23. Piston 27 has the same diameter as the flange extension 26.

Piston 28 is fixed to the cylindrical shell 29, in any convenient manner, such as by being made integral therewith or by being secured to the inner surface of the cylindrical shell 29 by bolts, or as illustrated, by welding. The outside diameter of the cylindrical shell 29 is the same as the inside diameter of the bushing or guide member 22, said cylindrical shell 29 being slideable between the bushing 22 and the flange extensions 26. O-rings 31 and 32, positioned within the bushing 22 and the flange extension 26, respectively, form a seal around the outside and inside, respectively, of the cylindrical shell 29.

The second reservoir 12 is defined by piston 28, the flange extension 26 and the cylindrical shell 29 extending therebetween. The opening in the center of the flange extension 26 permits communication between the second reservoir and the first reservoir through the passageway 13.

An opening 25 is positioned in the cylindrical shell 29 adjacent the piston 27 to permit communication between the interior of the chamber 35, defined by the flange extension 26, the piston 28 and the cylindrical shell 29, and the annular clearance 34 between the shell 29 and the inside of the side wall 17. The air is then permitted to exhaust to the atmosphere through the opening 21.

A check valve assembly 24, which may be similar to the ball check valve disclosed in my Patent No. 3,101,194, issued August 20, 1963, is used for permitting air and any other material to flow out of the interior of both reservoirs 11 and 12 when the internal pressure reaches a predetermined level.

An annular ring member 33 is rigidly secured to the outside of the cylindrical shell 29 at one end thereof. The thickness of the ring 33 is such that a slideable fit between it and the side wall 17 is established. O-rings 36 and 37 form a seal around the inside of the side wall 17 and the outside of the cylindrical shell 29, respectively.

The hollow post member 23 having an air passageway 13 connects the two reservoirs 11 and 12 together and thereby renders the pressure existing within them equal. The illustrated embodiment shows a sleeve 41 surrounding the hollow post 23. This serves the purpose of allowing for an inexpensive manufacture of the flange extension 26 by permitting a simply constructed counterbore 42 to receive the flange portion 43 on the hollow post member 23. This construction prevents axial movement in a downward direction. The sleeve 41 is of such a length that it extends from the inner surface of the flange extension 26 to the inner surface of the top wall 18. This type of construction prevents axial movement of the flange extension 26 in an upward direction. The upper portion of, the sleeve 41 is counterbored to create a cylindrical air passageway 43 between the center of the hollow post 23 and the sleeve 41. Transversely aligned holes 44 t permit air to pass from the air passageway 13 through the cylindrical air passageway 45 to the first reservoir 11.

Operation The pneumatic spring 10 is first inflated to its FIGURE 1 position by a pump (not shown) connected to the end of the supply line 15. Line pressure is admitted into the interior of the first and second reservoirs by the check valve assembly 14 thus filling the entire two volumes of the reservoirs 11 and 12. The pistons 27 and 28 are pushed downwardly by the line pressure until piston 27 is stopped by the flange extension 26. The pneumatic spring is then ready to cushion any load applied to it.

The mechanical load, represented by the arrow F, ap-

plied to the pneumatic spring 10 acts on the air trapped 4, tons 27 and 28 are acting upon the same body of air trapped inside the two reservoirs. Therefore, the pneumatic spring 10 is capable of withstanding twice the mechanical load as presently known pneumatic springs with little, if any, increase in the size of component parts. When the pneumatic spring is loaded and the pistons 27 and 28 begin to move upwardly, any air which may be trapped in the air chamber 35 is allowed to escape out through the opening 25, the annular clearance 34 and the opening 21 to the atmosphere when the volume therein decreases. This venting system is of significant importance because it permits air in the chamber 35, which air becomes heated during use of the spring by frictional and compressive effects, to be expelled when piston 27 is moved downwardly toward flange extension 26. Further, upon movement of piston 27 upwardly away from flange extension 26, fresh, cooler ambient air is drawn into the space. This tends to cool the entire unit and the operating life of the pneumatic spring is increased correspondingly.

There is no venting of the internal pressure during normal operation through the check valve assembly 24 the same being set at a value higher than the normal maximum operating pressure of the air within the device. However, as will usually happen, moisture condensation will collect in the reservoirs which reduces the volume available for air in the reservoirs. As a result, the air within said reservoirs occupies a smaller volume and this causes an increase in the pressure within the reservoirs. Thus, when the pressure reaches a predetermined level, air escapes through the check valve 24 and carries with it the water and/or other foreign material, it any, which has collected within the air chamber.

If for some reason, such as leakage, the air pressure within the pneumatic spring should become lower, the pressure is automatically restored by air pumped through the supply line 15, through the check valve assembly 14 and into the reservoirs 11 and 12.

Although particular preferred embodiments have been described above in detail for illustrative purposes, it will be recognized that variations or modifications of such disclosure, which come within the scope of the appended claims, are fully contemplated.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A pneumatic spring utiliz ng an elastic fluid as a resilient means comprising in combination:

housing means defining a first reservoir having a bottom wall, parallel side walls and an open end;

wall means;

hollow post means mounted on the bottom of said housing means -for supporting said wall means spaced from the bottom of said housing means;

a first piston slideable and sealed with respect to said side walls of said housing means positioned between said wall means and said bottom, a second piston spaced from said wall means on the opposite side thereof from said first piston and enclosure means slideable and sea-led with respect to said side walls of said housing means, said enclosure means rigidly connected to both of said first and second pistons and being in sliding and sealing engagement with said wall means, the interior of said hollow post means communicating with a second reservoir defined by said wall means and said second piston and that portion of said enclosure means between said wall means and said second piston;

means connecting the interior of said post to said first reservoir;

whereby a force applied to one of said pistons and bottom of said housing means will diminish the sizes of said first and second reservoirs and equally compress said elastic fluid located therein and when said force is removed, said compressed elastic fluid will cause said first and second reservoirs to return to their original sizes.

2. The device defined in claim 1 wherein said pistons, said wall means, said enclosure means and said side walls of said housing means are all of circular cross section.

3. The device defined in claim 1 wherein said enclosure means includes openings providing communication to the outside atmosphere from the zone between said wall means, said first piston and said enclosure means.

4. The device defined in claim 1 including means for supplying elastic fluid under constant pressure to said first reservoir.

5. In a spring utilizing an elastic fluid as the resiliently resistant means, the combination comprising:

means defining a main cylinder housing;

means supplying a compressible fluid to said main cylinder housing;

means defining a hollow movable piston unit slideably positioned within said main cylinder housing; wall means axially spaced from one end of said main cylinder housing and slideably positioned within said piston unit thereby defining two inner interdependent fluid-tight chambers;

means providing communication from the first of said fluid-tight chambers to the atmosphere;

means providing communication from the second of said fluid-tight chambers to said main cylinder hous- 20 whereby movement of said piston unit against the pres- 6 sure will compress said fluid within said second chamber and said main cylinder housing and thereby be resistant to compression of said fluid and whereby cooler ambient air may enter said means communicating with said first fluid-tight chamber to thereby cool said spring.

6. The device defined in claim 5, wherein said hollow movable piston unit comprises a pair of coaxial pistons interconnected by means defining a chamber therehetween.

7. The device defined in claim 5, wherein a clearance is provided between said hollow piston unit and said main cylinder housing; and

wherein said means providing communication from said first fluid-tight chamber to the atmosphere includes at least one passageway through said main cylinder housing to connect said clearance to said atmosphere and further includes at least one passageway through said hollow piston unit to connect said first fluid-tight chamber to said clearance. 

